A porous thin film has pores. With the absorption and separation functions and so on of the pores, the porous thin film can be used in various industrial fields, e.g., lithographic masks, antireflection materials, data-storage materials, catalysts, chemical sensors, functional materials, filters and separation films. Such a porous thin film is required to have regularly aligned pores and possess as many pores as possible.
Conventionally, a porous inorganic thin film has been made by using polystyrene beads and polymer latex in a size of 200 nm to 500 nm, colloid particles and opal particles in a micro size, and the like as a template. However, since pores of the porous inorganic thin film have a micro size or the size of 200 nm to 500 nm, the size of the pores needs to be further reduced.
There are two major methods for making a nano porous thin film. Firstly, once aluminum is anodically oxidized by an anodic oxidation method, regular pores having a several tens of nanometer diameter are formed on a surface of the aluminum. The spacing or the size of the pores can be adjusted through oxidation conditions. Secondly, a nanometer level of a porous structure can be made by microphase separation and self-assembly of a block copolymer. The size or the form of the pores can also be modified by controlling a molecular weight or block composition.
Since the latest porous thin film in a nanometer size has innumerable holes in a controlled (uniformed) size, the porous thin film is useful as a filter. With introduction of the functionality, the porous thin film may be used for separation or purification of a specific material, an enzyme fixture material, and so on.
However, a conventional method for producing a porous thin film uses complicated processes in producing the porous thin film. A size and distribution of pores formed on a produced porous thin film are irregular. Further, it is difficult to adjust the size and alignment of the pores.